A heat treatment method for improving the impact energy of the core of a thick-gauge 16MnDR low-temperature container steel plate

Abstract

The application discloses a heat treatment method for improving the impact energy of a thick-specification 16MnDR low-temperature container steel plate core, and the heat treatment method is subcritical quenching + high-temperature tempering; the quenching heating temperature is an austenite-ferrite two-phase zone, and the temperature is 880 DEG C; the steel plate is quenched to room temperature after being discharged; the tempering temperature is 510-530 DEG C; the chemical components of the steel plate are as follows in percentage by weight: C is 0.08-0.10%, Si is 0.20-0.30%, Mn is 1.40-1.60%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, Nb is 0.035-0.045%, V is 0.035-0.045%, Ti is 0.01-0.02%, and the balance is Fe and inevitable impurities. The application greatly improves the -40 DEG C core impact toughness of the thick-specification 16MnDR low-temperature container steel plate.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a heat treatment method for improving the impact energy of the core of a thick 16MnDR cryogenic container steel plate. Background Technology

[0002] 16MnDR is a cryogenic pressure vessel steel specified in GB / T713.3-2023. The standard requires normalized delivery and it is widely used in the petrochemical and coal chemical industries for manufacturing cryogenic pressure vessels. The steel plate is required to have good low-temperature impact toughness, corrosion resistance, good machinability, and weldability.

[0003] Regarding the low-temperature impact toughness of thick steel plates, users often require that the impact energy at both the 1 / 4 thickness and 1 / 2 thickness points be qualified at -40℃. Production practice shows that during the normalizing process of steel plates thicker than 50mm, the low-temperature impact energy at the 1 / 4 thickness point remains stable, while the impact energy at the 1 / 2 thickness point is unstable, resulting in a low pass rate and failure to meet standard requirements. This leads to substandard steel plates and consequently, losses for enterprises. Therefore, improving the low-temperature impact toughness of thick steel plates has become a technical challenge and innovation point in the research and development and production of 16MnDR pressure vessel steel.

[0004] Patent CN101876001A discloses a method for improving the low-temperature impact toughness of high-strength thick steel plates. By employing a quenching + quenching + tempering heat treatment process, the microstructure of the steel plate after secondary quenching is controlled to be a mixed structure of hard and soft phases, thus improving the low-temperature toughness of the steel plate. The drawback is that the use of two quenching processes significantly increases production costs.

[0005] Patent CN107760987A discloses a method for improving the low-temperature impact toughness of a 15CrMoR steel plate and its core. The method improves the core low-temperature impact toughness of thick 15CrMoR steel plates through preheating before normalizing and a normalizing + tempering heat treatment process. However, this method is only applicable to 15CrMoR steel plates and not suitable for other steel grades, and it also increases production costs.

[0006] Patent CN105420468A discloses a heat treatment method to ensure the low-temperature toughness of thick-gauge high-strength steel. This method improves the low-temperature toughness of thick-gauge high-strength steel through quenching, tempering, and secondary tempering. However, its drawbacks include its applicability only to this specific steel grade and the use of two tempering processes, which significantly increases production costs. Summary of the Invention

[0007] The purpose of this invention is to provide a heat treatment method for improving the core impact energy of thick 16MnDR cryogenic container steel plates, which greatly improves the core impact toughness of thick 16MnDR cryogenic container steel plates at -40℃, and stably controls the core impact energy of 16MnDR cryogenic container steel plates with a thickness greater than 50mm at -40℃ to above 150J, significantly improving the pass rate of core impact energy of thick steel plates.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] This invention discloses a heat treatment method for improving the core impact energy of thick 16MnDR cryogenic container steel plates, wherein the heat treatment method is sub-critical quenching + high-temperature tempering.

[0010] The heat treatment process described in this invention involves quenching at an austenite-ferrite two-phase temperature of 880±10℃, with a furnace time of 1.4min / mm×t mm+10~20min, where t is the thickness of the steel plate; after the steel plate is removed from the furnace, it is quenched to room temperature.

[0011] The tempering temperature is 510-530℃, and the furnace time is 2.3min / mm×t mm+40min, where t is the thickness of the steel plate.

[0012] The chemical composition of the steel plate, by weight percentage, is C: 0.08-0.10%, Si: 0.20-0.30%, Mn: 1.40-1.60%, P: ≤0.020%, S: ≤0.005%, Nb: 0.035-0.045%, V: 0.035-0.045%, Ti: 0.01-0.02%, with the balance being Fe and unavoidable impurities.

[0013] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.08%, Si: 0.21%, Mn: 1.44%, P: 0.012%, S: 0.002%, Nb: 0.038%, V: 0.040%, Ti: 0.015%, with the balance being Fe and unavoidable impurities.

[0014] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.08%, Si: 0.25%, Mn: 1.45%, P: 0.013%, S: 0.002%, Nb: 0.039%, V: 0.041%, Ti: 0.013%, with the balance being Fe and unavoidable impurities.

[0015] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.09%, Si: 0.25%, Mn: 1.50%, P: 0.011%, S: 0.002%, Nb: 0.040%, V: 0.038%, Ti: 0.014%, with the balance being Fe and unavoidable impurities.

[0016] Furthermore, the steel plate thickness is 56mm; after shot blasting, the steel plate undergoes heat treatment, with a quenching heating temperature of 880℃ and a furnace time of 98 minutes, followed by quenching to room temperature after removal from the furnace; then it undergoes tempering treatment, with a tempering temperature of 510℃ and a furnace time of 169 minutes, followed by air cooling after removal from the furnace.

[0017] Furthermore, the steel plate thickness is 60mm; after shot blasting, the steel plate undergoes heat treatment, with a quenching heating temperature of 880℃ and a furnace time of 104 minutes, followed by quenching to room temperature after removal from the furnace; then it undergoes tempering treatment, with a tempering temperature of 510℃ and a furnace time of 178 minutes, followed by air cooling after removal from the furnace.

[0018] Furthermore, the steel plate thickness is 65mm; after shot blasting, the steel plate undergoes heat treatment, with a quenching heating temperature of 880℃ and a furnace time of 111 minutes, followed by quenching to room temperature after removal from the furnace; then it undergoes tempering treatment, with a tempering temperature of 510℃ and a furnace time of 190 minutes, followed by air cooling after removal from the furnace.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] (1) Abandoning the original medium carbon composition design principle, the low carbon niobium vanadium titanium microalloying composition design was adopted, which fundamentally improved the quality of the billet and optimized the center segregation of the billet from C3.0 grade to C1.5 grade, thus ensuring the core impact qualification rate of thick steel plates from the source.

[0021] (2) Abandoning the original normalizing heat treatment method, the sub-temperature quenching + tempering heat treatment method is adopted, which greatly improves the low-temperature impact toughness of the core of 16MnDR low-temperature container steel plate. The impact energy of the core of 16MnDR low-temperature container steel plate with a thickness greater than 50mm at -40℃ is stably controlled above 150J, which significantly improves the pass rate of the impact energy of the core of thick steel plate.

[0022] (3) It created conditions for the stable production of thick-gauge pressure vessel steel plates using 250mm thick continuously cast slabs. Actual production and testing showed that its mechanical properties were excellent, solving the technical difficulties in the production of thick-gauge pressure vessel steel. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 The metallographic structure of the steel plate in Embodiment 1 of the present invention is shown.

[0025] Figure 2The metallographic structure of the steel plate in Comparative Example 1 of this invention is shown. Detailed Implementation

[0026] The present invention will be described in more detail below with reference to examples and comparative examples. These examples are merely descriptions of the best mode of implementation of the invention and do not limit the scope of the invention in any way.

[0027] Example 1

[0028] The chemical composition of the 16MnDR pressure vessel steel in Example 1 is shown in Table 1. The production process is as follows: hot metal pretreatment—converter smelting—LF refining—RH vacuum treatment—continuous casting—slab slow cooling—slab heating—high-pressure water descaling—rough rolling—finish rolling—Acc cooling, with a steel plate thickness of 56 mm. After shot blasting, the steel plate undergoes heat treatment, with a quenching temperature of 880℃ and a furnace time of 98 minutes, followed by quenching to room temperature after removal from the furnace. It then undergoes tempering treatment at 510℃ for 169 minutes, followed by air cooling after removal from the furnace. The steel plate properties are shown in Table 2.

[0029] Example 2

[0030] The implementation method is the same as in Example 1. The production process route is: hot metal pretreatment—converter smelting—LF refining—RH vacuum treatment—continuous casting—slab slow cooling—slab heating—high-pressure water descaling—rough rolling—finish rolling—Acc cooling. The steel plate thickness is 60mm. After shot blasting, the steel plate undergoes heat treatment. The quenching temperature is 880℃, the furnace time is 104 minutes, and after exiting the furnace, it is quenched to room temperature. Then, it undergoes tempering treatment at 510℃ for 178 minutes, and after exiting the furnace, it is air-cooled. The steel plate properties are shown in Table 2.

[0031] Example 3

[0032] The implementation method is the same as in Example 1. The production process route is: hot metal pretreatment—converter smelting—LF refining—RH vacuum treatment—continuous casting—slab slow cooling—slab heating—high-pressure water descaling—rough rolling—finish rolling—Acc cooling. The steel plate thickness is 65mm. After shot blasting, the steel plate undergoes heat treatment. The quenching temperature is 880℃, the furnace time is 111 minutes, and after exiting the furnace, it is quenched to room temperature. Then, it undergoes tempering treatment at 510℃ for 190 minutes, and after exiting the furnace, it is air-cooled. The steel plate properties are shown in Table 2.

[0033] Comparative Example 1

[0034] The chemical composition of the 16MnDR pressure vessel steel in Comparative Example 1 is shown in Table 1. The production process is as follows: hot metal pretreatment—converter smelting—LF refining—RH vacuum treatment—continuous casting—slab slow cooling—slab heating—high-pressure water descaling—rough rolling—finish rolling—Acc cooling, with a steel plate thickness of 56 mm. After shot blasting, the steel plate undergoes normalizing heat treatment at a heating temperature of 860℃ for 98 minutes, followed by air cooling after tapping. The steel plate properties are shown in Table 2.

[0035] Comparative Example 2

[0036] The implementation method is the same as Comparative Example 1. The production process route is: hot metal pretreatment—converter smelting—LF refining—RH vacuum treatment—continuous casting—slab slow cooling—slab heating—high-pressure water descaling—rough rolling—finish rolling—Acc cooling. The steel plate thickness is 60 mm. After shot blasting, the steel plate undergoes normalizing heat treatment at a heating temperature of 860℃ for 104 minutes, followed by air cooling after removal from the furnace. The steel plate properties are shown in Table 2.

[0037] Comparative Example 3

[0038] The implementation method is the same as Comparative Example 1. The production process route is: hot metal pretreatment—converter smelting—LF refining—RH vacuum treatment—continuous casting—slab slow cooling—slab heating—high-pressure water descaling—rough rolling—finish rolling—Acc cooling. The steel plate thickness is 65mm. After shot blasting, the steel plate undergoes normalizing heat treatment at a heating temperature of 860℃ for 111 minutes, followed by air cooling after removal from the furnace. The steel plate properties are shown in Table 2.

[0039] Table 1 Chemical composition (wt%) of the present invention

[0040] Example C Si Mn P S Nb V Ti 1 0.08 0.21 1.44 0.012 0.002 0.038 0.040 0.015 2 0.08 0.23 1.45 0.013 0.001 0.039 0.041 0.013 3 0.09 0.25 1.50 0.011 0.002 0.040 0.038 0.014 Comparative Example 1 0.16 0.28 1.42 0.013 0.002 0.055 Comparative Example 2 0.16 0.26 1.46 0.011 0.001 0.060 Comparative Example 3 0.17 0.30 1.50 0.010 0.001 0.061

[0041] The steel plates of Examples 1 to 3 of the invention were tested for conventional mechanical properties, impact properties, and bending properties. The results are shown in Table 2.

[0042] Table 2 Mechanical properties of the steel plates of this invention

[0043] Example Thickness (mm) Yield strength (MPa) Tensile strength (MPa) Elongation (%) <![CDATA[Charpy impact energy Kv2 (J) at 1 / 2 thickness in transverse direction at -40℃]]> 180° bending performance 1 56 436 567 29.5 244\233\294 qualified Comparative Example 1 56 422 548 31.0 23\37\19 qualified 2 60 396 534 31.5 271\326\243 qualified Comparative Example 2 60 438 567 29.5 56\63\36 qualified 3 65 400 536 30.5 256\222\218 qualified Comparative Example 3 65 432 557 30.0 23\35\105 qualified Agreement requires ≥36～80 ≥285 460～590 ≥21 ≥57 D=2a

[0044] Table 2 shows that the comparative example, produced using a medium-carbon composition design and conventional normalizing heat treatment, exhibits deteriorated impact performance at -40°C at half thickness due to severe banded structure in the core, uneven grain size, and low compression ratio. The impact energy is unstable and fails to meet standard requirements. Examples 1-3 demonstrate the performance of steel plates produced using this invention. Employing a low-carbon microalloying composition design and quenching and tempering heat treatment, the impact energy stability at -40°C at half thickness is significantly improved, solving the technical difficulties in producing 16MnDR low-temperature pressure vessel steel with a thickness greater than 50mm.

[0045] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A heat treatment method for improving the core impact energy of thick 16MnDR cryogenic vessel steel plates, characterized in that, The heat treatment method is sub-temperature quenching followed by high-temperature tempering. The quenching heating temperature is in the austenite-ferrite two-phase region, and the temperature is 880±10℃. The furnace time is 1.4min / mm×t mm+10~20min, where t is the thickness of the steel plate. After the steel plate is taken out of the furnace, it is quenched to room temperature. The tempering temperature is 510-530℃, and the furnace time is 2.3min / mm×t mm+40min, where t is the thickness of the steel plate. The chemical composition of the steel plate, by weight percentage, is C: 0.08-0.10%, Si: 0.20-0.30%, Mn: 1.40-1.60%, P: ≤0.020%, S: ≤0.005%, Nb: 0.035-0.045%, V: 0.035-0.045%, Ti: 0.01-0.02%, with the balance being Fe and unavoidable impurities.

2. The heat treatment method for increasing the core impact energy of thick 16MnDR cryogenic vessel steel plates according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.08%, Si: 0.21%, Mn: 1.44%, P: 0.012%, S: 0.002%, Nb: 0.038%, V: 0.040%, Ti: 0.015%, with the balance being Fe and unavoidable impurities.

3. The heat treatment method for improving the core impact energy of thick 16MnDR cryogenic vessel steel plates according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.08%, Si: 0.25%, Mn: 1.45%, P: 0.013%, S: 0.002%, Nb: 0.039%, V: 0.041%, Ti: 0.013%, with the balance being Fe and unavoidable impurities.

4. The heat treatment method for increasing the core impact energy of thick 16MnDR cryogenic vessel steel plates according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.09%, Si: 0.25%, Mn: 1.50%, P: 0.011%, S: 0.002%, Nb: 0.040%, V: 0.038%, Ti: 0.014%, with the balance being Fe and unavoidable impurities.

5. The heat treatment method for improving the core impact energy of thick 16MnDR cryogenic vessel steel plates according to claim 2, characterized in that, The steel plate is 56mm thick. After shot blasting, the steel plate is heat-treated by quenching at 880℃ for 98 minutes and then quenched to room temperature. After that, it is tempered at 510℃ for 169 minutes and then air-cooled.

6. The heat treatment method for improving the core impact energy of thick 16MnDR cryogenic vessel steel plates according to claim 3, characterized in that, The steel plate is 60mm thick. After shot blasting, the steel plate is heat-treated by quenching at 880℃ for 104 minutes and then quenched to room temperature. After that, it is tempered at 510℃ for 178 minutes and then air-cooled.

7. The heat treatment method for improving the core impact energy of thick 16MnDR cryogenic vessel steel plates according to claim 4, characterized in that, The steel plate is 65mm thick. After shot blasting, the steel plate is heat-treated by quenching at 880℃ for 111 minutes and then quenched to room temperature. After that, it is tempered at 510℃ for 190 minutes and then air-cooled.

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